1. Field of the Invention
The present invention relates to a solenoid-operated pump having an actuator such as a plunger electromagnetically movable back and forth, and more particularly to such a solenoid-operated pump for use in a burner in which pressurized fuel atomization is employed for normal fuel combustion.
2. Prior Art
Solenoid-operated pumps of the type described have an actuator reciprocable through, a small stroke at high speeds for effecting a pumping operation. With the small stroke of the actuator, the pump chamber undergoes a small change in volume. This has led to a disadvantage in that the pumping operation becomes inefficient when a great amount of air is trapped in the oil or fuel to be pumped especially at the time of starting operation of the pump or doing so after replenishing the fuel tank, since the trapped air is contractible in volume in the pump chamber. Accordingly, the fuel pressure becomes lower than the required degree in the fuel feeding system, thus preventing the fuel from getting atomized sufficiently at a spray nozzle with the result that incomplete or abnormal combustion will take place.
Such incomplete or abnormal combustion is disadvantageous especially in that it adversely affects the performance and service life of an oil-burning infrared-ray generator as shown in FIG. 1 of the accompanying drawings which the applicant has recently developed. More specifically, fuel supplied from a burner is combusted in a hollow furnace made of ceramic fiber to produce a high-temperature gas, which is introduced into a vertical red-heat tube made of metal network on the order of 70-mesh where the high-temperature gas is discharged outwardly through the meshes of the tube for generating infrared rays. When the incomplete or abnormal combustion takes place, smoke is given off in the furnace and becomes carbonized in the red-heat tube, resulting in formation of carbon which clogs the meshes of the red-heat tube. Accordingly, the red-heat tube is prevented from being heated uniformly and tends to be deformed due to undue combustion pressure, at which time the tube might be cracked to thereby allow leakage of combustion gas.
Attempts have been known to remove air from fuel in the fuel-feeding system.
One such proposal is directed to a manually-operated directional control valve disposed in an outlet passage and actuatable by the operator at the time of starting operation of the infrared ray generator or as desired to return discharged fuel back into the fuel tank until air is no longer contained in the fuel. After removal of air from the fuel, the valve is actuated again to connect the outlet passage to the spray nozzle. This arrangement is troublesome since the operator is required to actuate the valve each time it is necessary to do so. Sometimes, the operator may forget to operate the valve or may reinstate the valve before the air is completely removed from the fuel.
An attempt for an automatic air-bleeding operation would be to dispose a pressure switch in the fuel outlet passage, and branch off a portion of the outlet passage which is located downstream of the pressure switch into two passages leading respectively to the spray nozzle and the fuel tank and which contain corresponding solenoid valves. If the pressure in the outlet passage is below a predetermined degree, the solenoid valve in the passage leading to the spray nozzle would be closed and the other solenoid valve in the passage leading to the fuel tank would be opened, thereby allowing air-laden fuel to be returned to the fuel tank until air is removed from the fuel. If the outlet passage is pressurized above the predetermined degree, the solenoid valve in the passage to the spray nozzle would be opened with the solenoid valve in the passage to the fuel tank being closed, so that fuel can be introduced into the spray nozzle. However, such a structure would require separate pressure switches and solenoid valves which are expensive, large in size and need an increased expenditure of time and labor in the assembling operation.